Hydrocarbon conversion process



ttes l 2,905,620 HYDROCARBON lCONVERSION PROCESS Application November 23, 1955, Serial No. 548,717- A2 Claims. (Cl. 208-65) This invention relates to an improved method for effecting a high yield of high octane number gasoline. More specifically, the invention relates to an integrated and modified type of catalytic reforming operation and fractionation which permits obtaining high yields of high octanenumber gasoline from a gasoline or naphtha charge stock. v

'Ihe refining industry has recently been directing its research efforts toward the development of a practical method for the production of high octane gasolines as a result of the recent trends in the automotive industry which require unprecedented increases in gasoline quality at present and in the future.

One process which has achieved great commercial ac-v,

ceptance is the catlytic reforming process. In effecting the usual methods of catalytic reforming, naphthenes are dehydrogenated to aromatics, straight-chain or slightly branched paraflins are converted to more highly branchedchain parafiins, heavy paraiiins are converted to lighter parafiins and some paraiiins are aromatics. However, in the final product from the reforming operation, there are present some straight or slightly branched paraiiins which have low octane number and even some morev highly branched-chain paraifns which have relatively low octane numbers. In the process of my invention these lower octane number components are converted to higher octane number hydrocarbons by subsequent catalytic reforming operations. The bulk of the aromatics in the efuent from the reforming zone are separated therefrom by a fractionation, and a subsequent catalytic reforming operation is performed on the lower boiling fraction of the effluent from the catalytic reforming zone. ln addition, the eiuent from the second catalytic reforming zone is fractionated and the lower boiling fraction is subsequently reformed in a separate catalytic reforming zone. This scheme of fractionation and reforming converts most of the straightchain or branched-chain paraflins in the lower boiling fraction in the eiiiuent to the high octane number aromatics.

There has recently been disclosed and provided commercially, an improved reforming operation which utilizes a platinum-alumina-combined helogen catalyst under conditions which permit long periods of continuous operation without the need of regenerating or replacing the catalyst, or in other words provides a substantially nonregenerative process. This improved catalyst and operation has been set forth in my U.S. Patent No. 2,479,110, issued August 16, 1949. In connection with this improved reforming process, it is generally desirable to process full-boiling range gasolines or, gasoline fractions in the presence of hydrogen, at a pressure within the range of from about 50 to about 1000 pounds per square inch to insure a substantially non-regenerative operation with a minimum of carbon formation. Y

It is the principal object of the present invention to provide an improved combination operation which will dehydrocyclized to atent 2,905,620 Patented Sept. 22, 1959 -Cie gasoline or a fraction thereof.

lt is another object of the present invention to providean improved combination operation which will effect an improvement in octane number from the straightchain or branched-chain paraiiins present in the charge.

In one embodiment the present invention relates to a process which comprises subjectingl hydrogen and a gasoline fraction to catalytic reforming in a first catalytic reforming zone, introducing the effluent from said first reforming zone `.to a first fractionation zone, separately withdrawing from said first fractionation zone at least a high boiling fraction and a low boiling fraction, subjecting at least a portion of said low boiling fraction to catalytic reformingin a second catalytic reforming zone, introducing the eiuent from said second catalytic reforming zone to a second fractionation zone, separately withdrawing from said second fractionation at least a high rboiling fraction and a low boiling fraction, subjecting vat least a portion of said low boiling fraction to catalytic reforming in a third catalytic reforming zone and recoveringthe effluent from said third catalytic reforming zone.

In another embodiment the present invention relates to a process for producing an improved high octane gasoline from a hydrocarbon charge stock boiling within the gasoline range wich comprises subjecting said stock and hydrogen to catalytic reforming in a first catalytic reforming zone' at a pressure within the range of yfrom about 400 toabout 1000 pounds per square inch, a temperature within the range of from about 850 F. to

about 1000 F., a weight hourly space velocity within the range of from about 1.0 to about 20.0 and a hydrogen to a hydrocarbon mol ratio within the range of from about 0.5:1 to about 20:1, .introducing thereformate from s'aid first reforming zone to a rst fractionationzone, separately withdrawing from said fractionation zone at least a high boiling fraction anda low boiling fraction, subjecting at least a portion of said low boiling fraction to catalytic reforming in a second catalytic reforming zone at a pressure at least pounds per square inch lower than the pressure in said first catalytic reforming zone and at a weight hourly space velocity lower than that existing'in said first catalyic reforming zone, introducing the reformate from said second catalytic reformingzone to a second fractionation zone, separately withdrawing from said second fraction zone at least a high boiling fraction and a low boiling fraction, subjectingat least a portion of said low boiling fraction to catalytic reforming in a third catalytic reforming zone at a pressure at least pounds per squareV inch lower than said pressure in said second catalytic reforming zone, and combining at least a portion of the reformate from said third catalytic reforming zone with at least a portion of said high boiling fraction from said second fractionation zone and at least a portion of said high boiling fraction from said first fractionation zone. f

In a specific embodiment the present invention relates to a process which comprises subjecting a gasoline fraction to kcatalytic reforming in a first catalytic reforming zone at a temperature within the range of from about 850 F. to about 1000 F., a pressure of from about 400 tozabout 1000 pounds per square inch, a weight hourly space velocity within the range of from about 1.0 to about 20, with hydrogen at a hydrogen to hydrocarbon mol ratio of from about 0.5 :l to about 20:1, in;

by weight of platinum,rsub stream and`A effecting the separation thereof lto provide a gaseous hydrogen-containing stream and a liquid stream, introducing the liquid stream to a first fractionation zone and removing isohexane and lower boiling hydrocarbons and fractionating the remaining liquid into at least a high boiling fraction and a low Iboiling fraction, subjecting at least a portion of said low boiling fraction to catalytic reforming in a second catalytic reforming zone at a temperature within the range of from about 860 F. to about l-l0 F., a pressure at least 75 pounds per square inch lower than the pressure in said first catalytic zone and at a weight hourly space velocity lower than that existing in said first catalytic reforming zone, with hydrogen at a hydrogen to hydrocarbon mol ratio of from about 0.5 :1y to about 20:1, in the presence of a catalyst comprising alumina and from about 0.01% to about 1% by weight of platinum, subsequently cooling the resultant reformed stream from said second catalytic reforming zone and effecting the separation thereof to provide a gaseous hydrogen-containing stream and a liquid stream, introducing the liquid stream to a second fractionation Zone and removing isohexane and lower boiling hydrocarbons and fractionating the remaining liquid into at least a highboiling fractionand a low boiling fraction, subjecting at least a portion of said low boiling fraction to catalytic reforming in a third catalytic reforming zone at a temperature within the rangeV of from about 870 F. to about 1020 F., a pressure at least 100.pounds per square inch lower than said pressure in said second. catalytic reforming zone, a weight hourly space velocity lower than the weight hourly space velocity in said iirst catalytic reforming zone and within the range of from about 0.5 to about 15, with hydrogen at a hydrogen to hydrocarbon mol ratio of from about 0.511 toabout 20:1, in the presence of a catalyst comprising alumina and from about 0.01% to about 1% by weight of platinum, and combining at least a portion of the effluent from said third reforming zone with at least a portion of said high boiling fraction from said second fractionation zone and at least a portion of said high boiling fraction from said first fractionation zone.

Briey, the present invention provides a method for producing a high octane number gasoline from a hydrocarbon stockl boiling in the gasoline range which cornprises subjecting saidstock to reforming in the presence of hydrogen and a suitable reforming catalyst in a first reforming zone. In the iirst catalytic reforming zone naphthenes are catalytically dehydrogenated to aromatics.

lt` isalso preferred that the conditions and catalystv be" such that there is heavy parain hydrocracking, parain isomerization and paraffin dehydrocyclization. The resulting catalytically reformed stream is cooled andthe stream is passed to a first fractionation Zone. In the first fractionation zone a'separation of the resulting reformed stream is effected to provide a gaseous hydrogen-containing stream and a liquid stream. The separation of the gaseous.hydrogen-containing stream and the liquid stream maybe a asl'l type separation. The liquid stream is passed to a fractionator and therein fractionated to produce at least a high boiling fraction and a low boiling fraction. In some cases it is desirable to remove isohexane and lighter hydrocarbons from the liquid and to fractionate the remaining liquid, that is the normal hexane and heavier hydrocarbons into at least a low boiling fraction and a high boiling fraction. The re-V moval of the isohexane and the lighter fraction and the fractionationk of the normal hexane and heavier fractioninto a low boiling fraction and a highboiling fraction may be accomplished in aY single fractionator, however, when desired twofractionators may be used. The low boiling fraction, that is the low boiling fraction formed.,

ated to aromatics and there also again occurs paraffin isomerization and parain dehydrocyclization. The resulting catalytically reformed stream from the second reforming Zone is cooled and passed to a second fractionation Zone. The first step occurring in the second fractionation zone is again a flash separation to provide a gaseous hydrogen-containing stream and a liquid stream. The liquid stream is then passed to a second fractionator. In the second fractionator it is preferred that isohexane and lighter components be removed overhead and theremaining liquid, that is normal hexane and heavier hydrocarbons, be fractionated into at least alow boiling fraction and a high boiling fraction as hereinbefore mentionedffor the tirstfractionation zone. This fractionation may be accomplished in one or more fractionators. The low boiling fraction removed from the second fractionation zone, that is the low boiling fraction separated by fractionating the normal hexane and heavier fraction into at least a low boiling fraction and a high boiling fraction, is passed to a third catalytic reforming zone. In-the third catalytic reforming zone additional aromatics are formed by dehydrogenation of naphthenes and dehydrocyclizationof paraflins. There also again occurs some isomerization of parafflns. The reformed stream from the third catalytic reforming zone may then be stabilizedto removenormally gaseous components and the' liquid recovered as product. In another embodiment of the present invention at least a portion of the stabilized effluent from the third catalytic reforming zone iscombined with at least aV portion of the high boiling fraction from said second fractionation Zone and at least aA portion of the high boiling fraction from said iirst J fraction zone.

from fractionating the; normal hexane and .heavier frac tion,'is passed to a second catalytic reforming zoneyand is subjected toreforming in the presence of hydrogen and*y asuitable reformingv catalyst4 In the second catalytic reforming zone naphthenes aregcatalytically dehydrogenv As` hereinbefore mentioned the removal of the isohexane and lighter fraction before fractionating the liquid into at least a low boiling fraction and a high boiling fraction is only a preferred embodiment. It is essential, however, that the eiuent from the first and the second catalytic reforming zones be fractionated into at least a low boiling liquid fraction and a high boiling liquid fraction.

The charge stocks which may be reformed in accordance with my process comprise hydrocarbon fractions that boil within the gasoline range and that contain naphtlrenes and paraiiins. The preferred stocks are those consisting essentially of naphthenes and paraflins, although aromatics and minor amounts of olelins may be present. This preferred class includes straight-run gasoline, natural gasoline and the like. The gasoline fraction may be a full-boiling range gasoline having an initial boiling point Within the range of from about 50 F. to about 100 F. and having an end boiling point Within the range of from about-350 F. to about 425 F. or it may be a selected fraction thereof, which usually is a higher boiling fraction commonly referred to as naphtha and having an initial boiling point within the range of from about l50 F. to about 250 F. and an end boiling point within the range of from about 350 F. to about 425 F. Mixtures -of the various gasolines and/or gasoline fractions may also be used and thermally cracked and/or catalytically cracked gasolines maybe used as charging stock. However, when these unsaturated gasoline fractions are used, it is preferred that they be used either in admixture with a straight-run or natural gasoline fraction, or else hydrogenated prior to use.

The conditions in the first catalytic reforming zone should be such that substantial conversion to naphthenes to aromatics is induced, and it is also preferred that -hydrocracking of heavy parafflns is induced. The temperature in the first catalytic reforming zone is usually a temperature Within the range of from-about 850 F. to about l000 P. The Weight hourly space velocity is preferably within the range offrom about 1.0 to 20.0. The weight hourly space Vvelocity vis defined as the weight of oilper hour per weight pery catalystin. the reaction g ione. 'It is preferred that the reforming reaction in the rst reaction zone be conducted in the presence of hydrogen. In one embodiment of the process sufficient hydrogen will be produced in the catalytic reaction zone to furnish the hydrogen required in the process and, therefore, it may be unnecessary to introduce hydrogen from an external source or to recycle hydrogen in the process. However, it usually is preferred to introduce hydrogen from an external source, generally at the beginning of the operation, and to recycle hydrogen within the process in order to be assured of a sufficient hydrogen atmosphere. The hydrogen present in the first reaction zone preferably is such that the hydrogen to hydrocarbon mol ratio is within the range of from about 0.5:1 to about 20:1. Generally the conditions in the first reforming reaction zone are such that milder conditions are present than if it were attempted to reform the charge stock to high octane levels in a once-through operation. The total pressure in the reaction zone is within the range of from about 400 to about 1000 pounds per square inch.

It is preferred that the reforming operation in the first reforming zone be an operation in which a catalyst having a relatively long life is used. A platinum-aluminacombined halogen catalyst is preferred for use in each of the three catalytic reforming zones. The catalyst composition may vary from one catalytic reforming zone to the other, however, it generally is preferred to utilize the same catalyst composition in each of the reaction zones since this facilitates catalyst loading and catalyst reclaiming. Variations of desirable and suitable catalysts may be used in the first, second, and/0r third stages of the process, however, the preferred operation utilizes an improved platinum-alumina-combined halogen catalyst in each of the reaction zones. The catalyst that may be used in the catalytic reforming zones comprises those reforming catalysts that promote dehydrogenation of naphthenic hydrocarbons, hydrocracking of paraffinic hydrocarbons and dehydrocyclization of paraiiinic hydrocarbons. It is also preferred that the catalyst possess isomerization activity. A satisfactory catalyst comprises a platinum-alumina-silica catalyst of the type described in U.S. Patent No. 2,478,916, issued August 16, 1949. A preferred catalyst comprises a platinum-alumina-combined halogen catalyst of the type described in my U.S. Patent No. 2,479,109, issued August 16, 1949. Other catalysts such as platinum-alumina, molybdena-alumina, chromia-alumina, and platinum on a modified cracking catalyst base may be used.

The concentration of the platinum on the catalyst of the reaction zones may range up to about by Weight of the alumina but a desirable catalyst may be provided with to contain about 0.1 to about 1% by weight of the catalyst. The halogen ions may be present in the amount of from about 0.1% to about 8% by weight of the catalyst but preferably are present in an amount of from about 0.1% to about 3% by weight of the alumina on a dry basis. Also, while any of the halogen ions provides a desirable catalyst, the fluoride ions are particularly preferred and next in order are the chloride ions, the bromideions, and the iodide ions.

A fixed bed reforming operation is preferred for each of the catalytic reforming zones because the preferred catalysts to use in these zones comprise platinum-containing catalysts, and a fixed bed operation prevents loss of the relatively expensive catalyst. Further, it has been found that at the relatively mild conditions maintained in each of the zones, that the preferred catalyst may be employed for extended periods of time without regeneration or replacement, that is, an essentially non-regenerative process may be employed. This is of great economic advantage since fixed bed operations employ apparatus v which is relatively inexpensive compared to that employed in fluidized operations, and further the maintenance problems when using xed bed operations are markedlyl less than when using a iluidized operation.

Further, it has been found that fixed bed operations iii the catalytic reforming zone generally give better results. This may be due to the temperature' profile, that is, the temperature drop or rise through the catalyst bed which may be such that the desired reactions are promoted to a greater extent than when a uniform temperature is maintained throughout the catalyst bed. While a fixed bed operation is preferred in each of the catalytic reforming zones, it is to be understood that fluidized, fluidized-frxed bed, moving bed and/or slurry types of operation may also be used, however, not necessarily with equivalent results. Further one or more beds or reactors of catalyst may be used in each of the reforming zones.

A preferred operation effects the recycle of at least a portion of the hydrogen stream being separated from the reformed gasoline stream from each of the catalytic reforming zones, into contact with the charge streams to each of the respective catalytic reforming zones in order to provide added hydrogen to each of the catalytic reforming zones. A portion of the hydrogen separated from the effluent from the first reaction zone may be passed to the second catalytic reaction zone and/or the third catalytic reaction zone and likewise a portion of the hydrogen separated from the effluent from the second catalytic reaction zone may be introduced to the third reaction zone. Generally the conditions in each of the reforming zones are such that there is a net production of hydrogen.

I have discovered that when the eluent from the first catalytic reforming zone, before or after stabilization to remove normally gaseous components or to remove isohexane and lighter components, is fractionated into at least a low boiling fraction and a high boiling fraction, the high boiling fraction contains substantially all of the aromatics, or -that is more of the aromatics appear in the high boiling fraction than in the low boiling fraction. This may be due to the fact that a greater part of the naphthenes originally present in the stock were high boiling naphthenes or that it is easier to dehydrocyclicize the heavy parains to form aromatics than to dehydrocyclicize the low boiling paraiiins. Therefore, it is not economical to catalytically reform the higher boiling fraction again, since the catalytic reforming operation may, especially at higher temperatures, crack some of the high octane number aromatics to form lower octane number parafiins. My process, therefore, also has the economic advantage of catalytically reforming only a portion of the reformed streams from the first and second reforming zones, which requires smaller initial investment since only a smaller stream is subsequently catalytically reformed. The exact temperature at which the effluent from the first and second catalytic reforming zones, are split or fractionated into the low boiling fraction and the high boiling fraction depends, in general, upon the character of `the components in the catalytically reformed gasoline effluent streams respectively. I have, however, found that generally the low boiling fraction has an end point Within the range of from about 225 F. -to about 325 F. The initial boiling point of the heavy boiling fraction corresponds, generally, with the end point of the low boiling fraction, that is, the initial boiling point of the heavy fraction is Vwithin the range of from about 225 F. 'to about 325 F.

In accordance with the present invention, the efliuent from the iirst catalytic reforming zone is subjected to a fractionation in a first fractionation zone to fractionate the eluent into at least a low boiling normally liquid fraction and a high boiling normally liquid fraction. In some cases it is desirable to stabilize the efliuent from each of these reaction zones by removing normally gaseous components, that is C4 and lighter components, therefrom, and the stabilized effluent is fractionated into at least a low boiling fraction and high boiling fraction. In another embodiment of this invention the effluent from lthe catalytic reforming zone is separatedA into atleast au low boiling fraction and a high boiling fraction without an intermediate stabilization. Further, the stabilization and the fractionation `may beperformed in one fractionator; thatV is, for example, a C4 andk lighter fraction may be removed as overhead from a fractionator, which is the stabilization, anda light or low boiling fraction may be removed from an intermediate portion of the fractionator and a heavier fraction may be removed farther down Vthe column, for example, at the bottom thereof. Further, isohexane and lighter components are high in octane nurnberand are not substantially improved in octane numbercby a subsequent catalytic` reforming operation and it is, therefore, preferred to removetthe isohexane and lighter components and` to obtain lthe low boiling fraction and the high boiling fractionn by fractionation of the normal hexane and heavier material. The isohexane and pentanes, and in some cases, when desired the butanes, may berecovered and blended with one or more of the product streams.

In accordance with the present invention the iow boiling liquid fraction is introduced to a second catalytic reforming zone. This low boiling fraction has a low octane number and canbe substantially increased in octane number by a subsequent catalytic reforming operation. I have` discovered that the increase in octane number is much greater than if the low boiling components are reformed together with the high boiling fraction. A fractionation into at least a low boiling fraction and a high boiling fraction is, therefore, an essential part of my invention. The high boiling fraction is highly aromatic and by the fractionation these aromatics are eliminated from the charge to the second reaction zone. In order to obtain a substantial increase in octane number, however, it is necessary that the second reforming zone be maintained at a pressure at least 75 pounds per square inch and preferably at least 100 pounds per square inch lower than the pressure in said iirst reforming zone. The reason for the lower pressure is that as the molecular weight of the paraffins is reduced, their conversion into aromatics becomes more and more diiiicult and requires iower pressures. The fractionating out of the bulk of the aromatics in the effluent from the reaction zone by removal of the heavy fraction helps in forming aromatics in the second reaction zone since the low boiling components may now form aromatics without the chemical equilibrium restriction imposed by the presence of the aromatics, that is the chemical equilibrium has been shifted by the removal of aromatics so that more aromatics may now be formed. Also if the heavy aromatics were not removed in the fractionation, in a subsequent catalytic reforming operation, they would have a tendency to form heavy polynuclear aromatics which deposit as carbonaceous material on the catalyst and tend to deactivate the same.

Except for the lower pressure the conditions in the second reaction zone are substantially the same as in the first. It is preferred however that the weight hourly space velocity in the second zone be lower than in the rst so as to aid in converting the paraiiins into aromatics. For the same reason it is preferred that the temperature in the second zone be higher and within the range of from about 860 F. to about 1010 F. As hereinbefore mentioned, any suitable reforming catalyst such as one of the catalysts hereinbefore described may be used in the second reaction zone and the catalyst may be the same or different than that used in the second reaction zone.

The eiiiuent from the second reforming Zone is now introduced to a second fractionation zone and is therein subjected to the same or similar treatment as the eftiuent from the rst reaction zone, which operation has hereinbefore been described in detail. A low boiling liquid fraction and a high boiling liquid fraction are therefore removed from lthe second fractionation zone. The low boiling fraction is then introduced to a third catalytic reforming reaction zone.

This reforming of, the low boiling fraction of theefliuent from the second reforming reaction zone in a..V

third reforming reactionzone is an essential part of, myl invention. Previously, it was believed that after two reforming operations, that a hydrocarbon fraction could'` notbe substantially increased in octane number. I, however, have discovered that when the effluent from the reforming zone is fractionated into at least a 10W boiling fraction and alight boiling fraction, and the low boil-.

ing fraction is reformed in a third catalytic reforming.

zone at a lower pressure than that in the second reforming zone that the low boiling fraction is substantially increased in octane number. The pressure in the third reforming zone is at least pounds per square inc h lower than the pressure in the second, reforming zone. It is preferred that the temperature in the third zone beV higher than in the first and within the range of from.

about 870 F. to about 1020 F. It is also preferred that the weight hourly space velocity in the third reforming zone be lower than that in the ysecond reforming zone. The other operating conditions are within the ranges mentioned for the first zone. The catalyst for the third zone may be any suitable reforming catalyst such as any of the hereinbefore mentioned catalysts and,

subsequent fractionation and reforming of any fractionI- of the eiuent from the third reforming zone does not substantially increase the octane number and accordingly theoperation may be terminated at this point.

The eiuent from the third reaction zone may be cooled and passed to a third fractionation zone wherein normally gaseous components are removed, thereby stabilizing the eiiiuent. In a preferred embodiment of this invention at least a portion of the stabilized effluent from the third reaction zone is combined with at least a portion of the high boiling fraction from the lirst fractionation zone and atleast a portion of the high boiling fraction from the second fractionation zone. The blend is of high octane number and further the yield is higher than if this octane number were obtained by a once through severe operation.

Additional features and advantages of my invention will be apparent from the following description of the accompanying drawing which illustrates a particular method for conducting a gasoline reforming operation in accordance with the present invention. Although the process illustrated in the drawing represents one or more of the preferred forms of my invention, it is to be understood that my invention is not limited thereby. A number of variations may be introduced into the process without departing from the spirit and scope of the invention. For simplification, many valves, pumps, heat exchangers, etc. have been eliminated from the drawing as their illustration is not essential to an understanding of the invention.

Referring now to the drawing, there is indicated a straight-run gasoline fraction having an initial boiling point of 200 F. and au end point of 400 F. being passed through line 1, picked up by pump 2 and discharged into line 3 containing valve 4. A hydrogen-rich gas stream in line 5 mixes with the charge in line 3 and the combined stream in line 6 is passed into heater 7 wherein the combined stream is heated to a temperature ofV 905 VF. The heated combined stream is withdrawn from heater '7 by way of line S and passes into catalytic reforming reactor 9.

Reforming reactor 9 contains a bed off spherical catalyst of approximately Ms average diameter containing 0.5% platinum, 0.4% combined chlorine, the remainder being alumina. The pressure in the reactor is 500 pounds per square inch, the weight hourly space velocity is 4.0, and the hydrogen to hydrocarbon mol ratio is 8 to 1. During the passage #of the charge stock through reactor 9 the bulk of the naphthenes containing 6 or more carbon atoms per molecule are dehydrogenated to the corresponding aromatics and a portion of the parains are hydrocracked to lower boiling parafns. Some isomerization of the parains also takes place. In reference to the hydrocracking reaction, the higher boiling paraflins are usually much easier to crack than the lower boiling parafns at the conditions maintained in the rst catalytic reforming zone. Therefore, substantially all of the higher boiling parailins are hydrocracked to loWer boiling; paraiiins. Accordingly, the effluent from the catalytic reactor 9 is substantially free of higher boiling paraiins; and the parans contained in the eluen-t are chiefly the lower boiling paraiiins. The fractionation `step of my invention is based on this discovery. The important octane number increasing reaction of dehydrocyclization also occurs in reactor 9 at these conditions. By this reaction a substantial portion of the parains, especially the higher boiling parafns, are converted to aromatics. This reaction is extremely important in increasing the octane number of the parains. The conditions in the reforming zone or reactor 9 such that there are substantially no olenic hydrocarbons produced. While one reactor isl shown it is to be understood that the reaction Zone mayY be one or more reactors in series with interheating in; between.

The ellluent from reactor 9 passes through line 10 cooler 11, line 12 and into separator 13. Hydrogen is withdrawn from the top of receiver or separator 13; through line 14. Excess hydrogen may be withdrawnA through line 15 containing valve 16 and thence through. lines and 21 containing valve 22. A portion of the` hydrogen may pass through lines 20, 23, 36 and 37, into' heater 50, line 51 and into the second reaction zone 52.. At least a portion of the hydrogen in line 14 passes: through line 17, is picked up by compressor 18 and dis-- charged into line 5.

The liquid hydrocarbons, comprising the reformate and. i

the bulk of the normally gaseous hydrocarbons producech in the process, are withdrawn from receiver 13 throug'n line 24 and passed into fractionator 25. In fraotionator 25, isohexane and lighter components are removed overhead through line 26, pass through cooler 27 wherein a. portion of the material is condensed, and the entire streampasses through line 28 into receiver 30. In receiver 30i the liquid phase and the gas phase of the overhead mate-- rial separate. The gas passes through line 31 from which` it may be vented to the atmosphere or otherwise used.. Liquid may be withdrawn from receiver 38 through line: 29. The conditions in the fractionator are usually/ such that1C4 and lighter components are removed as overa head, however, as herein illustrated, the gasoline therein; may be cut deeper, specifically isohexane and lighter connponents are removed overhead through line 26. It is com.

templatcd that the fractionator 25 and receiver 30 willi i operate at a sutilcient pressure to liquefy at least a por,-v tion of the overhead material so that a liquid stream may be available to improve the separation in fractionator 25. The liquid reilux passes from receiver 30 through'n line 32 and into an upper portion of fractionator 25. The;

fractionator has heat provided thereto by reboiler 41 and;A connecting lines 40 and 42. A heavy fraction. is re-- moved from fractionator 25 by way of line 38. An inter-A mediate fraction having an initial boiling point of 156 F.. and an end point of 250'k F.. is withdrawn from an inter-A4 mediate section of fractienator 2S- through line 33., is: picked up by pump 34 and discharged through line 35.. The liquid in line 35 combines with hydrogen` being recycled through line 36. and. the combined stream in lirle 10 Y 37 passes into heater 50. In heater 50 the stream is heated to a temperature of 910 F. The heated stream is withdrawn from heater 50 through line 51 and introduced into reactor 52.

Reactor 52 is loaded with a catalyst of the type used l in the first reaction zone. In reactor 52, however, the conditions are more suitable for the dehydrocyclization reaction. A lower pressure, a higher temperature and a lower space velocity are therefore used. -In the embodiment illustrated, a pressure of 400 pounds per square inch, a weight hourly space velocity of 3.0 and a hydrogen to hydrocarbon mol ratio of 6 to 1 are used. The reformed gasoline stream from reactor 52 is withdrawn through line 53, passes through cooler 54, line 55, and into separator 56. In separator 56 a hydrogen-rich gas is removed overhead through line 57. The hydrogen in line 57 may be divided into several streams. An excess portion may be withdrawn through line 58 containing valve 59. Another portion may continue through lines 60 and 65, through valve 66 and into line 67. From line 67 the hydrogen ultimately enters the third reaction zone 87. At least a portion of the hydrogen continues from line 60 through line 61, is picked up by compressor 62 and .discharged through line 63. The liquid in receiver 56 is `withdrawn through line 69 and introduced into fractiona- Jtor 70. Fractionator 70 is operated the same as fractionator 25, however, it is not necessary that they be operated similarly. Fractionator 25 and/ or 70 may each be divided into two separate fractionators so that isohexane and lighter components are removed in one fractionator, with the split-up of the normal hexane and heavier hydrocarbons into a light fraction and a heavy fraction being accomplished in a second fractionator.

As illustrated in the drawing, however, the fractionation is accomplished in one fractionator. An isohexane and lighter stream is removed overhead through line 71, passes through cooler 72, line 73 and into receiver 74. 'The fractionator 70 and overhead receiver 74 are operated so as to condense at least a portion of the overhead material in receiver 74 so as to provide a liquid for redux -on column 70. In receiver 74 uncondensed material is removed overhead through line 75 while reflux is withrdrawn from receiver 74 through line 76 and introduced iinto an upper portion of fractionator 70. Heat is prowided for the fractionation in fractionator 70 by reboiler .79 and connecting lines 78 and 80. A high boiling fraction is withdrawn from fractionator 70 through line 68.

An intermediate fraction having an initial boiling point tof 156 F. and an end point of 235 F. is withdrawn from ifractionator 70 through line 77, is picked up by pump 81 and discharged into line 82. The liquid in line 82 combines with hydrogen being recycled through line 83 and the combined stream in line 84 passes into heater 85. -In heater S5 the combined stream is heated to a temperature of 930 F. The heated stream is withdrawn through line 86 and passes into reactor 87.

Reactor 87 is loaded with a catalyst similar to that used in the first and second reaction zones 9 and 52, respectively. The pressure and space velocity maintained in the third reaction zone 87 are lower than maintained in the second reaction zone 52 and the temperature is higher. .The pressure is 200 pounds per square inch and the weight hourly space velocity is 2.0, While the hydrogen to hydrocarbon mol ratio is 4 to 1. The reformed stream is withdrawn from reactor 87 through line 88, passes through cooler 89, line 90 and into separator 91. In separator 91 hydrogen-rich gas separates from the liquid and is withdrawn through line 92. A portion may be vented or withdrawn through line 96 containing valve 97. At least a portion, however, continues through line 93, is picked up by compressor 94 and discharged through line 95. The hydrogen in line 95 combines with the hydrogen in line 67 and the combined stream in line 83 'combines with the liquid charge in line 82 as hereinbe.. 75 riore described.

.The liquid from receiver or separator 91 is withdrawn",

tionator 99 `is maintained as a stabilizer and only C4 and 4 lighter components are removed as overhead, however, the gasoline therein may be cut deeper, thatpis, C and/ or Cs hydrocarbons may be removed overhead throughline 100, The overhead material in line 100 passes through cooler 101, line 102 and into receiver 103. Fractionator 99 and receiver 103 are operated at a suiiicient pressure to liquefy at least a portion of the overhead material so that a liquid stream may be available to improve the separation in fractionator 99. The liquid reux passes from receiver 103 through line 105, in-to an upper portion of fractionator 99. Gases may be removed from receiver 103 through line 104. Heat is provided for the fractionation in fractionator 99 by reboiler 111 and connecting lines 110 and 112. The stabilized gasoline fraction is removed from fractionator 99 through line 113.

ln a preferred embodiment of the present invention, the high boiling fraction from fractionator 25, which is removed through line 38, combines with the high boiling fraction from fractionator 70, which is removed through line 68, and this combined stream in line 106 is combined with the stabilized fraction in line 113 and the resultant combined strearn in line 114 is recovered as product.

The following examples are given to further illustrate the operability of the present invention, however, they are not introduced with the intention of unduly limiting the generally broad scope of the invention.

EXAMPLE I A desulfurized Mid-Continent straight-run gasoline having an end point of 325 F. was catalytically reformed in the presence of a catalyst comprising alumina, 0.4% platinum, and 0.5% combined fluorine. The conditions in the reforming zone were a pressure of` 600 pounds per square inch, 3.0 liquid hourly space velocity, and 8:1 hydrogen to hydrocarbon mol ratio. average catalyst temperature was about 880 F. The product from the catalytic reactor was fractionated to remove C5 and lighter components. rlhe remainder of the reformate wasV fractionated into several cuts, the boiling rangeV and F-l clear octane number ratings are given below in the table.

Table Boiling range: F-l clear octane number (D6-187 F 68.4 187 F.-234 F 68.2 234 F.-259 F 60.0 259 F.279 F 83.3 279 F.-286 F 91.7 286 F.322 F 84.1 322 F.-333 F 98.0

From the above table it may readily be seen that the low octane number components are predominantly in fractions boiling below 259 F. The lower boiling fraction may be improved in octane number by another catalytic reforming operation at a lower pressure. When the reformate from the second reforming operation is fractionated into cuts, it is again seen that the low octane number components are present in the lower boilingV fractions. A third reforming operation on the low boiling fraction at a still lower pressure again improves the octane number of the fraction.

EXAMPLE Il A straight-run gasoline fraction having an initial boiling point of 205 F. and an end point of 395 F. is subjected to reforming by passing the fraction through a reactor centrally located in an electrically heated furnace. The tube is filled with a catalyst containingV alumina, 0.5% by weight of lluorine and'O.5% by weight of platinum.- Hydosfsa is. also introduced into the reaction,

The

Zone. The reforming conditions maintained in the ref actor are, in average catalyst temperature of 890 F.,`

a pressure of 700 pounds per square inch, a weight` hourly space velocity of 4.5 and a hydrogen to hydro- I carbon mol ratio of 87:1.

The eiliuent from the reactor is fractionated to remove isohexane and lighter components. The normal hexane and heavier fraction is passed to a fractionator and fractionated into a low boiling fraction having an end point of285 F., and a high boiling fraction. The low boiling fraction is then subjected to catalytic reforming in the presence of a catalyst containing alumina, 0.5% by weight of lluorine and 0.5% by weight of platinum. Hydrogen is also introduced to this second reaction Zone. The reforming conditions in the second Zone are: pres sure, 450 pounds per square inch; temperature, 898 F.; weight hourly space velocity 3.0 and a hydrogen to hydrocarbon mol ratio of 7:1. This operation improves g the octane number of the low boiling fraction.

The effluent from this second reaction Zone is stabilized by removing isohexane and lighter components. The

normal hexane and heavier fraction is fractionated into a low boiling fraction having an end point of 275 F. and a high boiling fraction. The low boiling fraction is subjected to reforming in a third reforming zone in the ypresence of a catalyst of the same composition as used fractionating out C4 and lighter components. The octane number is much improved by this third reforming operation. The stabilized effluent is combined with both of the high boiling fractions separated from the eiuent from the first two reaction Zones. The mixture is a motor fuel of very high octane number and excellent starting characteristics.

I claim as my invention:

l. A process which comprises subjecting a gasoline fraction to catalytic reforming in a rst catalytic reforming Zone at a temperature within the range of from about 850 F. to about 1000 F., a pressure of from about 400 to about 1000 pounds per square inch, a weight hourly space velocity within the range of from about 1.0 to about 20, with hydrogen at a hydrogen to hydrocarbon mol ratio of from about 0.5:1 to about 20:1, in the presence of a catalyst comprising alumina and from about 0.01% to about 1% by weight of platinum, subsequently fractionating the resultant reformed stream and separating therefrom a high boiling gasoline fraction and a low boiling gasoline fraction, said low boiling fraction having an end point within the range of from about 225 F. to about 325 F., subjecting at least a portion of said low boiling fraction to catalytic reforming in a second catalytic reforming zone at a temperature within the range of from about 860 F. to about l0l0 F., a pressure at least 75 pounds per square inch lower than the pressure in said first catalytic zone and at a weight hourly space velocity lower than that existing in said first catalytic reforming zone with hydrogen at a hydrogen to hydrocarbon mol ratio of from about 0.5:1 to about 20:1, in the presence of -a catalyst comprising alumina and from about 0.01% to about 1% by weight of platinum, subsequently fractionating the resultant reformed stream from said second catalytic reforming zone and separating therefrom a high boiling gasoline fraction and a low boiling gasoline fraction, said low boiling fraction having an end point within the range of from about 225 F. to about 325 F., subjecting at least a portion of said low boiling fraction to catalytic reforming in a third catalytic reforming zone at a temperature within the range of from about 870 F. to about 1020 F., a pressure at least 100 pounds per square Yinch lower than said pressure in said second catalytic reforming zone, a weight hourly space velocity lower than the Weight hourly space velocity in said rst catalytic reforming zone and within the range of from about 0.5 to about 15, with hydrogen at a hydrogen to hydrocarbon mol ratio of from about 0.5:1 to about 20:1, in the presence of a catalyst comprising alumina and from about 0.01% to about 1% by weight of platinum, and combining at least a portion of the eluent from said third reforming zone with at least a portion of said high boiling fraction from said second fractionation zone and at least a portion of said high boiling fraction from said rst fractionation zone.

2. A process which comprises subjecting a gasoline fraction to catalytic reforming in a irst catalytic reforming zone at a temperature within the range of from about 850 F. to about l000 F., a pressure of from about 400 to about 1000 pounds per square inch, a weight hourly space velocity within the range of from about 1.0 to about 20, with hydrogen at a hydrogen to hydrocarbon mol ratio of from about 0.5:1 to about 20: 1, in the presence of a catalyst comprising alumina and from about 0.01% to about 1% by weight of platinum, subsequently cooling the resultant reformed stream and elfecting the separation thereof to provide a gaseous hydrogen-containing stream and a liquid stream, introducing the liquid stream to a first fractionation zone and removing isohexane and lower boiling hydrocarbons and fractionating the remaining liquid into at least a high boiling fraction and a low boiling fraction, said low boiling fraction having an end point within the range of from about 225 F. to about 325 F., subjecting at least a portion of said low boiling fraction to catalytic reforming in a second catalytic reforming zone at a temperature higher than in said first catalytic reforming zone and within the range of from about 860 F. to about 10l0 F., a pressure at least 75 pounds per square inch lower than the pressure in said first catalytic reforming zone and at a weight hourly space velocity lower than that in said first catalytic reforming zone, with hydrogen at a hydrogen to hydrocarbon mol ratio of from about 0.5:1 to about 20:1, in the presence of a catalyst comprising alumina and from about 0.01% to about 1% by weight of platinum, subsequently cooling the resultant reformed stream from said second catalytic reforming zone and effecting the separation thereof to provide a gaseous hydrogen-containing stream and a liquid stream, introducing the liquid stream to a second fractionation zone and removing isohexane and lower boiling hydrocarbons and 'fractionating the remaining liquid into at least a high boiling fraction and a low boiling fraction, said low boiling fraction having an end point within the range of from about 225 F. to about 325 F., subjecting at least a portion of said low boiling fraction to catalytic reforming in a third catalytic reforming zone at a temperature higher than in said second catalytic reforming zone and within the range of from about 870 F. to about' 1020 F., a pressure at least 100 pounds per square inch lower than said pressure in said second catalytic reforming zone, a weight hourly space velocity, lower than said weight hourly space velocity in said second catalytic reforming zone and within the range of from about 0.5 to about 15, with hydrogen at a hydrogen to hydrocarbon mol ratio of from about 0.5 :1 to about 20:1, in the presence of a catalyst comprising alumina and from about 0.01% to about 1% by weight of platinum, and combining at least a portion of the eluent from said third reforming zone with at least a portion of said high boiling fraction from said second fractionation zone and at least a portion of said high boiling fraction from said lrst fractionation zone.

References Cited in the ile of this patent UNITED STATES PATENTS 2,710,826 Werkart June 14, 1955 2,739,927 Doumani Mar. 27, 1956 2,740,751 Haensel et al Apr. 3, 1956 

1. A PROCESS WHICH COMPRISES SUBJECTING A GASOLINEACID FRACTION TO CATALYTIC REFORMING IN A FIRST CATALYTIC REFORMING ZONE AT A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 850*F. TO ABOUT 1000*F., A PRESSURE OF FROM ABOUT 400 TO ABOUT 1000 POUNDS PER SQUARE INCH, A WEIGHT HOURLY SPACE VELOCITY WITHIN THE RANGE OF FROM ABOUT 1.0 TO ABOUT 20, WITH HYDROGEN AT A HYDROGEN TO HYDROCARBON MOL RATIO OF FROM ABOUT 0.5:1 TO ABOUT 20:1, IN THE PRESENCE OF A CATALYST COMPRISING ALUMINA AND FROM ABOUT 0.01% TO ABOUT 1% BY WEIGHT OF PLATINUM, SUBSEQUENTLY FRACTIONATING THE RESULTANT REFORMED STREAM AND SEPARATING THEREFROM A HIGH BOILING GASOLINE FRACTION AND A LOW BOILING GASOLINE FRACTION, SAID LOW BOILING FRACTION HAVING AN END POINT WITHIN THE RANGE OF FROM ABOUT 225*F. TO ABOUT 325*F., SUNJECTING AT LEAST A PORTION OF SAID LOW BOILING FRACTION TO CATALYTIC REFORMING IN A SECOND CATALYTIC REFORMING ZONE AT A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 860*F. TO ABOUT 1010*F., A PRESSURE AT LEAST 75 POUNDS PER SQUARE INCH LOWER THAN THE PRESSURE IN SAID FIRST CATALYTIC ZONE AND AT A WEIGHT HOURLY SPACE VELOCITY LOWER THAN THAT EXISTING IN SAID FIRST CATALYTIC REFORMING ZONE WITH HYDROGEN AT A HYDROGEN TO HYDROCARBON MOL RATIO OF FROM ABOUT 0.5:1 TO ABOUT 20:1, IN THE PRESENCE OF A CATLAYST COMPRISING ALUMINA AND FROM ABOUT 0.01% TO ABOUT 1% BY WEIGHT OF PLATINUM, SUBSEQUENTLY FRACTIONATING THE RESULTANT REFORMED STREAM FROM SAID SECOND CATALYTIC REFORMING ZONE AND SEPARATING THEREFROM A HIGH BOILING GASOLINE FRACTION AND A LOW BOILING GASOLINE FRACTION, SAID LOW BOILING FRACTIONHAVING AN END POINT WITHIN THE RANGE OF FROM ABOUT 225*F. TO ABOUT 325*F., SUBJECTING AT LEAST A PORTION OF SAID LOW BOILING FRACTION TO CATALYTIC REFORMING IN A THIRD CATALYTIC REFORMING ZONE AT A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 870* F. TO ABOUT 1020*F., A PRESSURE AT LEAST 100 POUNDS PER SQUARE INCH LOWER THAN SAID PRESSURE IN SAID SECOND CATALYTIC REFORMING ZONE, A WEIGHT HOURLY SPACE VELOCITY LOWER THAN THE WEIGHT HOURLY SPACE VELOCITY IN SAID FIRST CATALYTIC REFORMING ZONE AND WITHIN THE RANGE OF FROM ABOUT 0.5 TO ABOUT 15, WITH HYDROGEN AT A HYDROGEN TO HYDROCARBON MOL RATIO OF FROM ABOUT 0.5:1 TO ABOUT 20:1, IN THE PRESENCE OF A CATALYST COMPRISING ALUMINA AND FROM ABOT 0.01% TO ABOUT 1% BY WEIGHT OF PLATINUM, AND COMBINING AT LEAST A PORTION OF THE EFFLUENT FROM SAID THIRD REFORMING ZONE WITH AT LEAST A PORTION OF SAID HIGH BOILING FRACTION FROM SAID SECOND FRACTIONATION ZONE AND AT LEAST A PORTIONOF SAID HIGH BOILING FRACTION FROM SAID FIRST FRACTIONATION ZONE. 